#9894: Group cohomology spkg, version 2.1.2
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Reporter: SimonKing | Owner:
Type: enhancement | Status:
positive_review
Priority: major | Milestone:
sage-5.0
Component: optional packages | Resolution:
Keywords: modular group cohomology solaris t2 | Work issues:
Report Upstream: N/A | Reviewers:
Karl-Dieter Crisman, John Palmieri
Authors: Simon King | Merged in:
Dependencies: | Stopgaps:
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Comment (by SimonKing):
Replying to [comment:63 jhpalmieri]:
> This looks great! Positive review.
Thank you very much! Finally, the old version (broken with recent Sage)
can be replaced!
> sage: (H0.2 * H0.3).is_zero()
> True
> sage: (H0.2 * H0.3) == 0
> False
> Maybe comparisons or `__eq__` need to be implemented, too.
I think that answers are consistent, for following reason:
* `H0.2*H0.3` is zero in the cohomology ''group'' H^2^(D8). As elements
in that group, they are zero, hence "is_zero()" returns True.
* However, even though they vanish and thus represent a relation of the
cohomology ring, they are still cocycles of degree 2. Thus, they are not
equal to `H0.zero_element()`, which is a cocycle of degree 2. Hence, the
comparison with the zero of the cohomology ''ring'' returns False.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/9894#comment:64>
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